1. Field of the Invention
The present invention relates to an electromagnetic driving device having a construction adapted for driving the diaphragm blades of a diaphragm device of, for example, a camera or the like.
2. Description of Related Art
Heretofore, electromagnetic driving devices using electromagnetic driving motors as drive sources, such as an electromagnetic driving diaphragm device which uses a stepping motor as a drive source, have been arranged, as disclosed in Japanese Laid-Open Patent Application No. HEI 3-207254, for example, to have a stator yoke and a coil arranged in one unit to extend in two radial directions with respect to the rotation axis of a rotor (two-phase type). Such a stepping motor has a shape that protrudes with respect to the diaphragm device.
In the stepping motor, a rotor shaft which is a motor output shaft protrudes from the stepping motor. A rotation output member such as a gear is provided on the protruding rotor shaft. Generally, the electromagnetic driving diaphragm device is thus arranged to drive a working member which drives diaphragm blades by the rotation of the gear on the rotor shaft.
In the above-stated example of conventional arrangement, the electromagnetic driving motor, i.e., a stepping motor, is arranged to protrude with respect to the diaphragm device. The protruding arrangement, however, hinders efforts to reduce the size of products and is thus against the recent trend of reduction in size. In other words, in the case of the stepping motor of the type disclosed in Japanese Laid-Open Patent Application No. HEI 3-207254, the stator yoke and the coil are arranged to extend in two radial directions with respect to the axis of rotation of the rotor (two-phase type). Therefore, the motor part flatly protrudes over a wide area for the diaphragm device. In a case where the layout of a camera or like product necessitates some other part to be also disposed in the motor space, therefore, the design of the camera or the like must be changed to avoid the use of the motor space for the part. Then, the change tends to cause the structural arrangement of the product to become complex or hinder reduction in size of the product.
In respect to the structural arrangement of the electromagnetic driving motor, the motor is of the type having a rotor shaft protruding therefrom. Therefore, the protruding part of the motor is supported only on its one side in a cantilever-like (or in an overhanging-impeller-like) manner, although the rotor is supported on its two sides within the electromagnetic driving motor (in a center impeller-like manner). Since the working member is under some amount of load, when a rotation force is transmitted to the working member under such a condition, some force is applied to the gear of the rotor shaft in its radial direction by a reaction to the load. This force exerts some lateral pressure on the rotor shaft to warp the free end side of the cantilever-like-supported rotor shaft.
Meanwhile, a force acts to restore the rotor shaft to its normal state against the warping force caused by the load of the working member. When the rotor shaft is caused to rotate under this condition, the rotor shaft comes to rotate in a whirling manner. Then, vibrations are transmitted to the working member within the diaphragm device. As a result, a chattering sound or chattering vibration arises there.
Such a chattering sound or chattering vibration has an adverse effect on the recent trend of arranging cameras or the like to make no sound and deteriorates the quality of the products. Besides, since a concentrated stress is applied to the bearing of the rotor by the lateral pressure on the rotor shaft, the performance of the motor is lowered by the stress.
Further, since the working member which drives the diaphragm blades within the diaphragm device rotates at high speed, the lateral pressure on the rotor shaft becomes very large to make the above-stated problems more serious.